Airedale Ultima Remote Air Cooled 75kW - 450kW - Manual (Page 10)

ULTIMA
™ REMOTE AIR COOLED
Chillers
10
Chillers
Technical Manual : Part No 6259485 V1.6.0_07_2014
Design Features & Information
ENERGY EFFICIENCY
Electronic Expansion
Valves (EEV) Whilst offering versatile control at the full design duty of the chiller, standard Thermostatic
Expansion Valves (TEV) do not automatically optimise themselves to all operating
conditions. Therefore, if the chiller is operating at 40% or 50% of full load, especially at a
lower ambient temperature than that for which the valve was sized, the conventional TEV
must have the design head pressure available to ensure good refrigerant control.
Maintaining an artificially high condensing pressure is normal in conventional systems,
however, this leads to higher operating costs.
Using an EEV allows for good refrigeration control with the chiller operating at part load
and lower ambient conditions with a reduced condensing pressure. By fitting an EEV and
adjusting the head pressure control setting, reduction in energy running values of up
to 27% can be achieved. The Mollier diagram shown below helps to illustrate how this
increase in efficiency is achieved.
EEV’s differ to normal thermostatic expansion valves in their ability to maintain control of
refrigerant flow and the suction superheat at reduced head pressures. The turn-down rate
of a typical EEV is superior to that of it’s thermostatic equivalent, such that a reduced
optimum condensing pressure can be maintained at low compressor load. However low
the load is on the compressor, from zero to 100%, there will not be a problem with turn
down, even below 30% rated capacity.
Pr
ess
u
re
(B
a
r)
Enthalpy
(kJ/kg)
Bubble Curve
Reduction In
Condensing
Temp
Evaporating
Temp
Dew Curve
Reduction in
Compressor
Input Power
Increase in
Cooling Duty
Ex
p
a
n
s
io
n
Heat of Rejection
Cooling Effect
Key
Cooling Cycle @ 22°C ambient with a conventional TEV fitted.
Cooling cycle @ 22°C ambient, demonstrating a typical EEV
condensing temperature taking full advantage of lower ambient air
temperatures (below 30°C).